Non-carboxylated styrene-butadiene copolymers, preparation method and use thereof

ABSTRACT

A non-carboxylated styrene-butadiene copolymer, preparation method and use thereof are provided. The non-carboxylated styrene-butadiene copolymer is prepared by hot polymerization in the absence of acid monomers and is used in asphalt-based systems such as asphalt emulsions.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/393,189, filed Oct. 14, 2010, which is incorporated herein byreference in its entirety.

BACKGROUND

Styrene-butadiene polymer dispersions are useful in the production ofseveral products, including vehicle tires, carpet backing, adhesives,foams, paper coatings and asphalt emulsions. There are two commonmethods for producing styrene-butadiene copolymer dispersions: a lowtemperature method (i.e., cold polymerization) and a high temperaturemethod (i.e., hot polymerization). The low temperature method ofproducing styrene-butadiene copolymer dispersions involves polymerizingstyrene and butadiene monomers at temperatures typically between 5° C.and 25° C. in the presence of a surfactant and in the absence of acarboxylated acid comonomer to produce a “cold” styrene butadiene rubber(SBR) copolymer. The low temperature method can be used to make highmolecular weight polymers without introducing excess crosslinking.Unlike the low temperature method, the high temperature method forproducing styrene-butadiene copolymer dispersions involves polymerizingstyrene and butadiene monomers at temperatures in excess of 40° C., andgenerally in the range of 50-95° C., in the presence of a surfactant anda carboxylated acid monomer.

The low temperature method of producing styrene-butadiene copolymerdispersions has generally been used for producing styrene-butadienepolymer dispersions for many of the above-described uses because it canbe agglomerated to produce a high solids content dispersion typically inexcess of 65% solids and can be crosslinked (i.e., cured) to increasethe tensile strength of the SBR without significantly reducing itselongation. The hot polymerization method, on the other hand, generallyis believed to be only useful for producing styrene-butadiene copolymerdispersions having a narrow particle size distribution and a solidscontent below 55% making the dispersions useful for products such aspaper coatings where polymer solids greater than 60% are not requiredand where the presence of carboxylation provides latex particlestability in the high shear environments encountered in the productionof such products. Therefore, the hot polymerization method has generallyonly been desirable for paper coatings and some low solids pressuresensitive adhesive applications.

One issue with low temperature SBR aqueous dispersions is that theygenerally cannot be used in hot mix asphalt formulations such as thoseused in road paving and asphalt shingle applications. Hot mix asphaltformulations for road paving must comply with the requirements set forthin the Strategic Highway Research Program (SHRP) including having adesired dynamic shear modulus and stiffness. High molecular weightnon-carboxylated SBR aqueous dispersions produce an undesired increasein viscosity of the hot mix asphalt formulation, making it difficult touniformly apply the formulation to a surface. Low molecular weightnon-carboxylated latex polymers can produce lower viscosity hot mixasphalt formulations; however, they do not have the desired SHRPperformance properties.

SUMMARY

A styrene-butadiene copolymer, a method of making a styrene-butadienecopolymer, and methods and compositions including a styrene-butadienecopolymer are disclosed. The styrene-butadiene copolymer is made using ahigh temperature method at a temperature of 40° C. or greater resultingin a styrene-butadiene copolymer comprising styrene and butadienemonomer units. The copolymer does not include acid monomer units, i.e.,is non-carboxylated and is cured (vulcanized) such as by using a sulfurcuring agent. The copolymer can include cis-1,4 butadiene units in anamount greater than 20% and trans-1,4 butadiene units in an amount lessthan 60% of the total number of butadiene units in the copolymer. Insome embodiments, the weight ratio of styrene to butadiene monomer unitsin the copolymer is 20:80 to 80:20. The copolymer can be derived fromonly styrene and butadiene monomers or can include other monomers (e.g.,acrylonitrile or acrylamide) or molecular weight regulators. In someembodiments, the copolymer has a soluble portion that has aweight-average molecular weight of less than 400,000 g/mol or less than200,000 g/mol and a number-average molecular weight of less than 20,000g/mol, as measured by Gel Permeation Chromatography (GPC). In someembodiments, the copolymer can have a gel content of from 0% to 40% orfrom 70% to 100%. The copolymer can be provided in an aqueous dispersionand modified to have an overall cationic charge.

A method of making a styrene-butadiene copolymer is also disclosed,comprising polymerizing styrene and butadiene in an aqueous medium at atemperature of 40° C. or greater to produce an uncured styrene-butadienecopolymer, wherein the polymerizing step occurs in the absence of acidmonomers and said method further includes the step of curing thestyrene-butadiene copolymer with a sulfur-based curing agent to producea cured non-carboxylated styrene-butadiene copolymer. In someembodiments, the method further includes the step of curing thestyrene-butadiene copolymer with the sulfur-based curing agent toproduce a cured non-carboxylated styrene-butadiene copolymer. In someembodiments, the polymerizing step occurs at a temperature of 50° C. orgreater. The polymerizing step can include only styrene and butadienemonomers or can include other monomers (e.g., acrylonitrile) ormolecular weight regulators. The resulting copolymers can haveweight-average molecular weights, number-average molecular weights andgel contents as described above. The method can also include the step ofmodifying the copolymer dispersion to have an overall cationic charge.In some embodiments, the polymerization occurs in a single stageprocess.

A blend of copolymers is also disclosed comprising the high temperaturepolymerized styrene-butadiene copolymer and a second styrene-butadienecopolymer. In some embodiments, the second styrene styrene-butadienecopolymer can be a higher molecular weight styrene-butadiene copolymerpolymerized at a temperature of less than 40° C. The blend ofstyrene-butadiene copolymers can be provided in water as an aqueousdispersion. For example, the blend can be prepared by mixing an aqueousdispersion comprising a first high temperature polymerizedstyrene-butadiene copolymer and an aqueous dispersion of the secondstyrene-butadiene copolymer. In some embodiments, the blend is curedafter the mixing of the styrene-butadiene copolymers. In someembodiments, the first styrene-butadiene copolymer dispersion can haveat least one first surfactant and the second styrene-butadiene copolymerdispersion can have at least one second surfactant, wherein the at leastone first surfactant and the at least one second surfactant can includeat least one common surfactant.

A polymer-modified asphalt composition is also disclosed includingasphalt and the high temperature styrene-butadiene copolymer. In someembodiments, the asphalt composition is substantially free of water andcan have, for example, a viscosity of less than 2000 cp at 135° C. Insome embodiments, the asphalt composition further comprises water andthe asphalt and the styrene-butadiene copolymer are dispersed in thewater with a surfactant to form an asphalt emulsion. The asphaltcomposition can have the styrene-butadiene copolymer present in anamount of from 0.5% to 30% based on the total solids content of thestyrene-butadiene copolymer and the asphalt. The asphalt composition canhave a second styrene-butadiene copolymer. In some embodiments, thesecond styrene-butadiene copolymer can have a weight ratio of styrene tobutadiene monomer units of 20:80 to 80:20 and can be polymerized at atemperature of less than 40° C.

A method of producing a polymer-modified asphalt is also disclosed,comprising blending asphalt and an aqueous dispersion of the hightemperature polymerized styrene-butadiene copolymer at a blendingtemperature exceeding the boiling point of water. For example, theblending temperature can be 150° C. or greater. The polymer-modifiedasphalt can have a second styrene-butadiene copolymer. In someembodiments, the second styrene-butadiene copolymer can have a weightratio of styrene to butadiene monomer units of 20:80 to 80:20 and can bepolymerized at a temperature of less than 40° C.

A method of producing a polymer-modified asphalt emulsion is alsodisclosed comprising providing an aqueous asphalt emulsion and mixingthe asphalt emulsion and an aqueous dispersion of the high temperaturepolymerized styrene-butadiene copolymer. In some embodiments, theaqueous dispersion can further include a second styrene-butadienecopolymer, for example, a copolymer having a weight ratio of styrene tobutadiene monomer units of 20:80 to 80:20 and polymerized at atemperature of less than 40° C. In some embodiments, the aqueousdispersion of the styrene-butadiene copolymer (optionally including thesecond styrene-butadiene copolymer) can be agglomerated to increase thesolids content.

The styrene-butadiene copolymer described herein can provide both thedesired performance and viscosity for use in hot mix asphalt systems.The styrene-butadiene copolymer can be used alone or blended with otherstyrene-butadiene copolymers in either cured or uncured systems.Furthermore, curing the styrene-butadiene copolymer produces only aminimal increase in viscosity when used in hot mix asphalt systems. Thestyrene-butadiene copolymer when used in asphalt emulsions impartsexcellent elastic recovery and sweep performance to asphalt residuesrecovered from the emulsions that have been modified by the copolymer.

DETAILED DESCRIPTION

As described herein, the styrene-butadiene copolymer is made using ahigh temperature method by polymerizing monomers comprising styrene andbutadiene (i.e., 1,3-butadiene) at a temperature of 40° C. or greaterresulting in a styrene-butadiene copolymer comprising styrene andbutadiene monomer units. The weight ratio of styrene to butadienemonomers used in the polymerization of the copolymer can be from 1:99 to99:1 or from 20:80 to 80:20. The weight ratio can be 25:75 or greater,30:70 or greater, 35:65 or greater, or 40:60 or greater. The weightratio can be 70:30 or less, 60:40 or less, 50:50 or less, 40:60 or less,or 30:70 or less. In some embodiments, the weight ratio of styrene tobutadiene monomer units in the copolymer is 25:75.

The copolymer is non-carboxylated and does not include acid monomerunits. The copolymer can be derived from only styrene and butadienemonomers or can be derived from other monomers, i.e., include othermonomer units. In some embodiments, the copolymer includes 10% or lessby weight of other monomer units. For example, the copolymer can includeat least one additional conjugated diene monomer (e.g., isoprene) ornatural rubber. The copolymer can also include at least one additionalvinyl aromatic monomer such as a-methylstyrene or o-chlorostyrene. Othersuitable monomers include acrylonitrile, methacrylonitrile, acrylamide,and methacrylamide. In some embodiments, the one or more additionalmonomers can include at least one (meth)acrylic acid ester. For example,methyl, ethyl, n-butyl, isobutyl and 2-ethylhexyl acrylates andmethacrylates can be used.

The copolymer can also include crosslinking monomers such asdivinylbenzene. The crosslinking monomers when used in the copolymer canbe present in an amount of from 0.2 to 5% and are considered part of thetotal amount of monomers used in the copolymer.

In some embodiments, the copolymer includes only styrene and butadienemonomer units, and optionally divinylbenzene monomer units. In someembodiments, the copolymer includes only styrene, butadiene andacrylonitrile monomer units, and optionally divinylbenzene monomerunits. In some embodiments, the copolymer can have a T_(g) of greaterthan −80° C. and less than 0° C.

As the copolymer is produced by high temperature polymerization, thecopolymer includes more cis-1,4 butadiene units than cold polymerizationstyrene-butadiene copolymers. In some embodiments, the copolymer caninclude cis-1,4 butadiene units in an amount greater than 20% andtrans-1,4 butadiene units in an amount less than 60% of the total numberof butadiene units in the copolymer. In some embodiments, the copolymercan include cis-1,4 butadiene units in an amount greater than 30% andtrans-1,4 butadiene units in an amount less than 55% of the total numberof butadiene units in the copolymer.

In some embodiments, the copolymer has a soluble portion intetrahydrofuran (THF) solvent that has a weight-average molecularweight, as measured by Gel Permeation Chromatography (GPC), of less than400,000 g/mol, less than 350,000 g/mol, less than 300,000 g/mol, lessthan 250,000 g/mol, less than 200,000 g/mol, less than 150,000 g/mol, orless than 100,000 g/mol. In some embodiments, the copolymer has anumber-average molecular weight, as measured by Gel PermeationChromatography (GPC), of less than 20,000 g/mol, less than 19,000 g/mol,less than 18,000 g/mol, less than 17,000 g/mol, less than 16,000 g/mol,less than 15,000 g/mol, less than 14,000 g/mol, or less than 13,000g/mol. The copolymer can have a polydispersity of 25 to 50, from 30 to45, or from 34 to 42.

Copolymers with either low or high gel content, in combination with arange of molecular weight values, are provided herein. In the someembodiments, the copolymers have a low gel content (e.g., from 0% to40%). For example, the gel content can be less than 40%, less than 30%,less than 25%, less than 20%, less than 15%, less than 10%, less than5%, or 0%. The soluble portion of the copolymer can have a molecularweight as described above.

In the some embodiments, the copolymers have a high gel content (e.g.,from 70% to 100%). For example, the gel content can be greater than 70%,greater than 75%, greater than 80%, greater than 85%, or greater than90%, or greater than 95%. The soluble portion of the copolymer (if any)can have a molecular weight as described above.

In some examples, the styrene-butadiene copolymer can be crosslinked orcured (i.e., vulcanized) using a sulfur curing agent as described inmore detail herein. Additional crosslinking or curing agents can be usedsuch as divinylbenzene; 1,4-butanediol diacrylate; methacrylic acidanhydride; monomers containing 1,3-diketo groups (e.g.,acetoacetoxyethyl(meth)acrylate or diacetonacrylamide); and monomerscontaining urea groups (e.g., ureidoethyl (meth)acrylate,acrylamidoglycolic acid, and methacrylamidoglycolate methyl ether); andsilane crosslinkers (e.g., vinyl triethoxysilane, 3-methacryloxypropyltrimethoxysilane and 3-mercaptopropyl trimethoxysilane). Additionalexamples of crosslinkers include epoxy functionalized (metha)acrylatemonomers (e.g., glycidyl methacrylate), N-alkylolamides ofα,β-monoethylenically unsaturated carboxylic acids having 3 to 10 carbonatoms and esters thereof with alcohols having 1 to 4 carbon atoms (e.g.,N-methylolacrylamide and N-methylolmethacrylamide); glyoxal basedcrosslinkers; monomers containing two vinyl radicals; monomerscontaining two vinylidene radicals; and monomers containing two alkenylradicals. Exemplary crosslinking monomers include diesters or triestersof dihydric and trihydric alcohols with α,β-monoethylenicallyunsaturated monocarboxylic acids (e.g., di(meth)acrylates,tri(meth)acrylates), of which in turn acrylic acid and methacrylic acidcan be employed. Examples of such monomers containing two non-conjugatedethylenically unsaturated double bonds are alkylene glycol diacrylatesand dimethacrylates, such as ethylene glycol diacrylate, 1,3-butyleneglycol diacrylate, 1,4-butylene glycol diacrylate and propylene glycoldiacrylate, vinyl methacrylate, vinyl acrylate, allyl methacrylate,allyl acrylate, diallyl maleate, diallyl fumarate andmethylenebisacrylamide. In some examples, the styrene-butadiene-basednon-carboxylated copolymers can include from 0 to 5% by weight of one ormore crosslinking monomers.

The styrene-butadiene copolymer can be provided in an aqueousdispersion. The styrene-butadiene copolymer dispersion can include oneor more natural or synthetic anionic surfactants. The copolymerdispersions can have a solids content of 40% to 75%. The dispersions canhave a solids content of 45% or greater, 50% or greater, 55% or greater,60% or greater, or 65% or greater. The polymer dispersion can have anaverage particle size of 200 nm or less or 100 nm or less (e.g., 20-100nm). The copolymer dispersion can have an overall anionic charge. Insome embodiments, the copolymer dispersion can be “flipped” to modifythe charge of the copolymer dispersion to have an overall cationiccharge by adding one or more cationic surfactants. Suitable cationicsurfactants include, for example, REDICOTE® E-5 (Akzo Nobel, Chicago,Ill.), REDICOTE® E-11 (Akzo Nobel, Chicago, Ill.), REDICOTE® E-53 (AkzoNobel, Chicago, Ill.), REDICOTE® E-606 (Akzo Nobel, Chicago, Ill.),REDICOTE® E-5127 (Akzo Nobel, Chicago, Ill.), ADOGEN® 477HG (ChemturaCorp., Greenwich, Conn.), INDULINO W-1 (MeadWestvaco, Charleston, S.C.),INDULINO W-5 (MeadWestvaco, Charleston, S.C.), INDULINO SBT(MeadWestvaco, Charleston, S.C.), and INDULINO MQK (MeadWestvaco,Charleston, S.C.). A non-ionic surfactant can also be used with thecationic surfactant. Suitable non-ionic surfactants include theTETRONIC™ and PLURONIC™ series of ethylene oxide-propylene oxide blockcopolymer surfactants sold by BASF Corporation, nonyl phenolethoxylates, octylphenol ethoxylates, dodecyl phenol ethoxylates, linearalcohol ethoxylates, branched alcohol ethoxylates such as tridecylalcohol ethoxylates, alcohol ethoxylates, block copolymers, PEG estersand castor oil ethoxylates.

The styrene-butadiene copolymer can be provided in an aqueous dispersionwith at least one additional styrene-butadiene copolymer, for example,by mixing a first aqueous dispersion including the high temperaturepolymerized styrene-butadiene copolymer described above with a secondaqueous dispersion including the additional styrene-butadiene copolymer.In some embodiments, at least one of the surfactants present in thefirst styrene-butadiene copolymer dispersion is the same as at least oneof the surfactants in the second styrene-butadiene copolymer dispersion.In some embodiments where the styrene-butadiene copolymers are to becured, the first styrene-butadiene copolymer dispersion and the secondstyrene-butadiene copolymer dispersion can be mixed prior to curing orone or both of the individual styrene-butadiene copolymer dispersionscan be cured prior to mixing. In some embodiments where thestyrene-butadiene copolymer dispersions are to be agglomerated, thefirst styrene-butadiene copolymer dispersion and the secondstyrene-butadiene copolymer dispersion can be mixed prior toagglomeration or one or both of the individual styrene-butadienecopolymer dispersions can be agglomerated prior to mixing. Further, insome embodiments where the styrene-butadiene copolymer dispersions areto be flipped, the first styrene-butadiene copolymer dispersion and thesecond styrene-butadiene copolymer dispersion can be mixed prior toflipping or both of the individual styrene-butadiene copolymerdispersions can be flipped prior to mixing.

The additional styrene-butadiene copolymer can be polymerized at a hightemperature or can be polymerized at a low temperature at less than 40°C., e.g., at 5 to 25° C. In some embodiments, the additionalstyrene-butadiene copolymer is polymerized at a low temperature. Theadditional styrene-butadiene copolymer can have a styrene to butadienemonomer weight such as those described above for the high temperaturestyrene-butadiene copolymers described herein. The additionalstyrene-butadiene copolymer can also include additional monomers such asthose described above for the high temperature styrene-butadienecopolymers described herein. The additional styrene-butadiene copolymercould also include acid monomer units, although low temperature SBR'swill typically not include acid monomer units. In some examples, theadditional styrene-butadiene copolymer can be crosslinked or cured usinga sulfur curing agent. The additional styrene-butadiene copolymer caninclude cis-1,4 butadiene units in an amount less than 20% and trans-1,4butadiene units in an amount greater than 60% of the total number ofbutadiene units in the copolymer. The additional styrene-butadienecopolymer can have a higher gel content (e.g., greater than 25%) and canhave a soluble portion that has a weight-average molecular weight, asmeasured by Gel Permeation Chromatography (GPC), of greater than 400,000g/mol, greater than 450,000 g/mol, or greater than 500,000 g/mol.

The high temperature polymerized styrene-butadiene copolymer can beprepared by polymerizing styrene and butadiene monomers in an aqueousemulsion polymerization reaction at a temperature greater than 40° C.,greater than 50° C., or greater than 60° C. or at a temperature lessthan 100° C., less than 90° C. or less than 80° C. The high temperaturepolymerized styrene-butadiene copolymer can be produced using either acontinuous, semi-batch (semi-continuous) or batch process. In someexamples, the high temperature polymerized styrene-butadiene copolymeris produced using a continuous method by continuously feeding one ormore monomer streams, a surfactant stream and an initiator stream to oneor more reactors. The monomers in the one or more monomer streams can befed at the desired butadiene to styrene weight ratio. A seed latex canalso be initially charged to the reactor. In some embodiments, thepolymerizing method using the high temperature polymerizedstyrene-butadiene copolymer can be produced using a single stagepolymerization, e.g., through the use of a single reactor. In addition,uniform copolymer particles can be produced (and not block copolymers).In some embodiments, the polymerization method is performed in theabsence of organic solvents such as N-methylpyrrolidone.

The surfactant stream includes a surfactant and water and can, in someembodiments, be combined with the initiator stream. The surfactant inthe emulsion stream can be a synthetic or natural surfactant. Forexample, the surfactant can be a natural surfactant such as sodium orpotassium oleate or the sodium or potassium salt of rosin acid. Thesurfactant can be present in the reactor in an amount from 0.5 to 5weight percent, based on total monomer weight.

At a polymerization temperature of 70° C. or greater, a thermalinitiator can be used in the reactor such as ammonium persulfate,potassium persulfate, or sodium persulfate. At temperatures of less than70° C., the thermal initiator can be combined with or replaced by aredox initiator comprising a free radical generator, a reducing agentand an activator (e.g., a water-soluble metal salt).

Suitable free radical generators include organic peroxygen compoundssuch as benzoyl peroxide, hydrogen peroxide, di-t-butyl peroxide,dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, decanoyl peroxide,lauroyl peroxide, diisopropylbenzene hydroperoxide, cumenehydroperoxide, p-methane hydroperoxide, a-pinene hydroperoxide, t-butylhydroperoxide, acetyl acetone peroxide, methyl ethyl ketone peroxide,succinic acid peroxide, dicetyl peroxydicarbonate, t-butylperoxyacetate, t-butyl peroxymaleic acid, t-butyl peroxybenzoate, andthe like; and alkyl perketals, such as 2,2-bis-(t-butylperoxy)butane,ethyl 3,3-bis(t-butylperoxy)butyrate, or 1,1-di-(t-butylperoxy)cyclohexane. In some embodiments, the free radical generator includesdiisopropylbenzene hydroperoxide or p-methane hydroperoxide. The freeradical generator is typically present in an amount between 0.01 and 1%by weight based on total monomer weight.

Suitable reducing agents for use in the initiator stream include sulfurdioxide; alkali metal disulfites; alkali metal and ammonium hydrogensulfites; thiosulfate, dithionite and formaldehyde sulfoxylates;hydroxylamine hydrochloride; hydrazine sulfate; glucose and ascorbicacid. For example, the reducing agent can include sodium formaldehydesulfoxylate dihydrate (SFS), sodium metabisulfite, or a mixture thereof.The reducing agent can be present in an amount between 0.01 and 1% byweight based on total monomer weight. In addition, the weight ratio ofreducing agent to free radical generator can be between 0.2:1 and 1:1.

The water-soluble metal salt can be an iron, copper, cobalt, nickel,tin, titanium, vanadium, manganese, chromium or silver salt and can bechosen from a wide variety of water-soluble metal salts. Suitablewater-soluble metal salts include copper (II) amine nitrate, copper (II)metaborate, copper (II) bromate, copper (II) bromide, copperperchlorate, copper (II) dichromate, copper (II) nitrate hexahydrate,iron (II) acetate, iron (III) bromide, iron (III) bromide hexahydrate,iron (II) perchlorate, iron (III) dichromate, iron (III) formate, iron(III) lactate, iron (III) malate, iron (III) nitrate, iron (III)oxalate, iron (II) sulfate pentahydrate, cobalt (II) acetate, cobalt(II) benzoate, cobalt (II) bromide hexahydrate, cobalt (III) chloride,cobalt (II) fluoride tetrahydride, nickel hypophosphite, nickeloctanoate, tin tartrate, titanium oxalate, vanadium tribromide, silvernitrate, and silver fluosilicate. The metal can also be complexed with acompound, such as ethylenediaminetetraacetic acid (EDTA) to increase itssolubility in water. For example, iron/EDTA complexes or cobalt/EDTAcomplexes can be used. The water-soluble metal salt can be present in anamount less than 0.01% by weight based on total monomer weight.

The polymerization reaction can be conducted in the presence ofmolecular weight regulators to reduce the molecular weight of thecopolymer. Suitable molecular weight regulators include C8 to C12mercaptans, such as octyl, nonyl, decyl or dodecyl mercaptans. In someembodiments, tert-dodecyl mercaptan is used as a molecular weightregulator. The amount of tert-dodecyl mercaptan used will depend uponthe molecular weight that is desired for the copolymer. In someembodiments, the amount of molecular weight regulator is from 0.01 and4% by weight (e.g., 0.1 to 1% by weight) based on total monomer weight.

The one or more monomer feeds, surfactant feed and initiator feed can beseparately fed to a reactor where polymerization of the styrene andbutadiene monomers occurs. The total amount of water in the reactors canbe 60-75% by weight based on total monomer weight. The emulsionpolymerization reaction normally produces between 60% and 80% conversionof the styrene and butadiene monomer into the styrene-butadienecopolymer particles.

Once the desired level of conversion is reached, the polymerizationreaction can be terminated by the addition of a shortstop to thereactor. The shortstop reacts rapidly with free radicals and oxidizingagents, thus destroying any remaining initiator and polymer freeradicals and preventing the formation of new free radicals. Exemplaryshortstops include organic compounds possessing a quinonoid structure(e.g., quinone) and organic compounds that may be oxidized to aquinonoid structure (e.g., hydroquinone), optionally combined with watersoluble sulfides such as hydrogen sulfide, ammonium sulfide, or sulfidesor hydrosulfides of alkali or alkaline earth metals; N-substituteddithiocarbamates; reaction products of alkylene polyamines with sulfur,containing presumably sulfides, disulfides, polysulfides and/or mixturesof these and other compounds; dialkylhydroxylamines;N,N′-dialkyl-N,N′-methylenebishydroxylamines; dinitrochlorobenzene;dihydroxydiphenyl sulfide; dinitrophenylbenzothiazyl sulfide; andmixtures thereof. In some embodiments, the shortstop is hydroquinone orpotassium dimethyl dithiocarbamate. The shortstop can be added in anamount between 0.01 and 0.1% by weight based on total monomer weight.However, the high temperature polymerization can be allowed to continueuntil complete monomer conversion, i.e., greater than 99%, in which casea shortstop may not be employed.

As mentioned above, the high temperature polymerized styrene-butadienecopolymer can also be produced using a batch process. In the batchprocess, the monomers, the surfactant, the free radical generator andwater are all added to a reactor and agitated. After reaching thedesired polymerization temperature, an activator solution if desired,that includes the reducing agent and the water soluble metal salt ifdesired can be added to initiate polymerization.

If a semi-batch process is used, the monomers, the surfactant in anaqueous solution, and the free radical generator in an aqueous solutionare all fed to a reactor over a period of time, usually from 3 to 6hours. If desired, an activator solution that includes a reducing agentand/or a water soluble metal salt can also be added in the reactor priorto commencing the other feeds or can be fed over a time interval to thereactor. The high temperature polymerized styrene-butadiene copolymer ispreferably allowed to complete monomer conversion, i.e., greater than99%, in which case a shortstop may not be employed. However, ashortstop, if desired, can be added to terminate the polymerization ifthe desired conversion level is less than 99%.

Once polymerization is terminated (in either the continuous, semi-batchor batch process), the unreacted monomers can be removed from the latexdispersion. For example, the butadiene monomers can be removed by flashdistillation at atmospheric pressure and then at reduced pressure. Thestyrene monomers can be removed by steam stripping in a column. Theresulting SBR copolymer dispersion at this point typically has a solidscontent of less than 50%.

The SBR copolymer dispersion can be agglomerated, e.g., using chemical,freeze or pressure agglomeration, and water removed to produce a solidscontent of greater than 50% to 75%. In some embodiments, the solidscontent is 55% or greater, 60% or greater, or 65% or greater. Asdescribed above, the high temperature SBR copolymer dispersion can beblended with an additional SBR copolymer dispersion prior toagglomeration. The agglomerated particles result in a polymer dispersionof larger particles with a broader particle size distribution. Theagglomerated particles as described herein have a particle size of 100nm to 5 μm. For example, the particle size can range from 100 nm to 2 μmor from 200 nm to 1 μm. The co-agglomerated dispersion, even onceconcentrated, can have a viscosity that allows it to readily flow (i.e.,it does not gel). For example, an aqueous dispersion having a solidscontent greater than 60% can have a viscosity of less than 1000 cp at20° C. The agglomeration of the high temperature polymerizedstyrene-butadiene copolymer dispersion can be performed when the SBRcopolymer dispersion is in anionic form (prior to flipping).

An antioxidant can be added to the SBR latex dispersion to preventoxidation of the double bonds of the SBR polymer, and can either beadded before or after vulcanization of the SBR latex. The antioxidantscan be substituted phenols or secondary aromatic amines. Exemplarysubstituted phenols include 2,6-di-t-butyl-p-cresol (DBT);4,4′-thiobis(6-t-butyl-m-cresol); 3-t-butyl-4-hydroxyanisole (3-BHT);2-t-butyl-4-hydroxyanisole (2-BHT);2,2-methylenebis(4-methyl-6-t-butylphenol) (MBMBP);2,2-methylenebis(4-ethyl-6-t-butylpheno1) (MBEBP);4,4′-butylidenebis(3-methyl-6-t-butylpheno1) (SBMBP);2,2-ethylidenebis(4,6-di-t-butylphenol);2,6-di-t-butyl-4-sec-butylphenol; styrenated phenol;styrenated-p-cresol;1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenol)butane;tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenol)propionate]methane;n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate; triethyleneglycol bis[3-(3-t-butyl-5-methyl-4-hydroxy-phenyl)propionate];1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene;2,2′-dihydroxy-3,3′-di(a-methylcyclohexyl)-5,5′-dimethyldiphenylmethane; 4,4-methylenebis(2,6-di-t-butylphenol);tris(3,5-di-t-butyl-4-hydroxyphenol);tris(3,5-di-t-butyl-4-hydroxyphenyl) isocyanurate; 1,3,5tris(3′,5′-di-t-butyl-4-hydroxybenzoyl) isocyanurate;bis[2-methyl-4-(3-n-alkylthiopropionyloxy)-5-t-butylphenyl]sulfide;1-oxy-3-methylisopropylbenzene; 2,5-dibutylhydroquinone;2,2′-methylenebis(4-methyl-6-nonylphenol); alkylated bisphenol;2,5-di-t-amylhydroquinone; polybutylated bisphenol-A; bisphenol-A;2,6-di-t-butyl-p-ethylphenol;2,6-bis(2′-hydroxy-3-t-butyl-5′-methylbenzyl)-4-methylphenol;1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate;terephthaloyl-di(2,6-dimethyl-4-t-butyl-3-hydroxybenzyl sulfide);2,6-t-butylphenol; 2,6-di-t-butyl-2-dimethylamino-p-cresol;2,2′-methylenebis(4-methyl-6-cyclohexylphenol); hexamethylene glycolbis(3,5-t-butyl-4-hydroxyphenyl) propionate;(4-hydroxy-3,5-di-t-butylanilino)-2,6-bis(octylthio)-1,3,5-triazine;2,2-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate];N,N′-hexamethylene(3,5-di-t-butyl-4-hydroxycinnamide);3,5-di-t-butyl-4-hydroxybenzylphosphoric acid diethyl ester;2,4-dimethyl-6-t-butylphenol; 4,4′-methylenebis(2,6-di-t-butylphenol);4,4′-thiobis(2-methyl-6-t-butylphenol);tris[2-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate;2,4,6-tributylphenol; bis[3,3-bis(4′-hydroxy-3′-t-butylphenyl)butyricacid]glycol ester; 4-hydroxymethyl-2,6-di-t-butylphenol; andbis(3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide. Exemplary secondaryaromatic amines include N-phenyl-N′-isopropyl-p-phenylenediamine;N-phenyl N′-(1,3-dimethylbutyl)-p-phenylenediamine;N,N′-diphenyl-p-phenylenediamine; dioctyl-diphenylamine;dibetanaphthyl-p-phenylenediamine; 2,2,4-trimethyl-1,2-dihydroquinolinepolymer and diaryl-p-phenylenediamine. In addition, sulfur containingantioxidants such as dilauryl thiodipropionate, distearylthiodipropionate and 2-mercapto-benzimidazole; phosphorus containingantioxidants such as distearylpentaerythritol diphosphite; nickelcontaining antioxidants such as nickel diisobutyldithiocarbamate, nickeldimethyldithiocarbamate and nickel di-n-butyldithiocarbamate;2-mercaptotoluimidazole; zinc 2-mercaptotoluimidazole; and1,11-(3,6,9-trioxaundecyl)bis-3-(dodecylthio)propionate can be used. Theantioxidant can be provided in an amount from 0.1 to 5.0 percent or from0.5 to 2.0 percent by weight based on the weight of the SBR copolymer.

Antiozonants can also be added to the SBR copolymer dispersion toprevent ozone present in the atmosphere from cracking the SBR, bycleaving the double bonds of the SBR polymer. Typical antiozonantsinclude waxes (e.g., VANWAX™ H commercially available from R. T.Vanderbilt Co., Inc.) and N,N′-alkylaryl, N—N′ dialkyl and N,N′-diarylderivatives of p-phenylenediamine such asN,N′-di(2-octyl)-p-phenylenediamine,N,N′-di-3(5-methylheptyl)-p-phenylenediamine,N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (e.g., ANTOZITE™ 67Pcommercially available from R. T. Vanderbilt Co., Inc.),N-isopropyl-N′-phenyl-p-phenylenediamine, andN-cyclohexyl-N′-phenyl-p-phenylenediamine. The antiozonants can beprovided in an amount from 0.5 to 10 percent, from 1 to 5 percent, orfrom 1.5 to 3 percent, by weight based on the weight of the SBRcopolymer.

Prevulcanization inhibitors can also be added to the SBR dispersion toprevent premature vulcanization or scorching of the SBR polymer. Forexample, N-cyclohexylthio-phthalimide; phthalic anhydride;N-cyclohexyl-thiophthalimide; N-phenyl-N-(trichloromethylsulfenyl)-benzene sulfonamide; bis-(sulfonamido)-sulfides orpolysulfides (e.g., bis-(N-methyl-p-toluenesulfonamido)-disulfide);substituted thiophosphoramides (e.g.,N-cyclohexylthio-N-phenyldiethylphosphoramide); N-(sulfenyl)methacrylamides; thio-substituted-1,3,5-triazine, -diamine or-triamines; 2-(thioamino)-4,6-diamino-1,3,5-triazines; N,N′-substitutedbis-(2,4-diamino-s-triazin-6-yl)-oligosulfides; and substitutedthioformamidines can be used as prevulcanization inhibitors. In someembodiments, the prevulcanization inhibitor isN-cyclohexylthio-phthalimide (SANTOGARD™ PVI commercially available fromFlexsys) or N-phenyl-N-(trichloromethyl sulfenyl)benzene sulfonamide(VULKALENT™ E commercially available from Bayer). The prevulcanizationinhibitor is typically provided in an amount from 1 and 5 percent orfrom 1.5 to 3 percent by weight based on the weight of the SBR polymer.

The SBR dispersion can be vulcanized or cured to crosslink the SBRpolymer thereby increasing the tensile strength and elongation of therubber by heating the SBR, typically in the presence of vulcanizingagents, vulcanization accelerators, antireversion agents, and optionallycrosslinking agents. Exemplary vulcanizing agents include various kindsof sulfur such as sulfur powder, precipitated sulfur, colloidal sulfur,insoluble sulfur and high-dispersible sulfur; sulfur halides such assulfur monochloride and sulfur dichloride; sulfur donors such as4,4′-dithiodimorpholine; selenium; tellurium; organic peroxides such asdicumyl peroxide and di-tert-butyl peroxide; quinone dioximes such asp-quinone dioxime and p,p′-dibenzoylquinone dioxime; organic polyaminecompounds such as triethylenetetramine, hexamethylenediamine carbamate,4,4′-methylenebis(cyclohexylamine) carbamate and4,4′-methylenebis-o-chloroaniline; alkylphenol resins having a methylolgroup; and mixtures thereof. In some examples, the vulcanizing agentsinclude sulfur dispersions or sulfur donors. The vulcanizing agent canbe present from 0.1 to 15%, from 0.3 to 10%, or from 0.5 to 5%, byweight based on the weight of the SBR polymer.

Exemplary vulcanization accelerators include sulfenamide-typevulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, N-t-butyl-2-benzothiazole sulfenamide,N-oxyethylene-2-benzothiazole sulfenamide,N-oxydiethylene-2-benzothiazole sulfenamide,N-oxydiethylene-thiocarbamyl-N-oxydiethylene sulfenamide,N-oxyethylene-2-benzothiazole sulfenamide andN,N′-diisopropyl-2-benzothiazole sulfenamide; guanidine-typevulcanization accelerators such as diphenylguanidine,di-o-tolylguanidine and di-o-tolylbiguanidine; thiourea-typevulcanization accelerators such as thiocarboanilide, di-o-tolylthiourea,ethylenethiourea, diethylenethiourea, dibutylthiourea andtrimethylthiourea; thiazole-type vulcanization accelerators such as2-mercaptobenzothiazole, dibenzothiazyl disulfide,2-mercaptobenzothiazole zinc salt, 2-mercaptobenzothiazole sodium salt,2-mercaptobenzothiazole cyclohexylamine salt,4-morpholinyl-2-benzothiazole disulfide and2-(2,4-dinitrophenylthio)benzothiazole; thiadiazine-type vulcanizationaccelerators such as activated thiadiazine; thiuram-type vulcanizationaccelerators such as tetramethylthiuram monosulfide, tetramethylthiuramdisulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide anddipentamethylenethiuram tetrasulfide; dithiocarbamic acid-typevulcanization accelerators such as sodium dimethyldithiocarbamate,sodium diethyldithiocarbamate, sodium di-n-butyldithiocarbamate, leaddimethyldithiocarbamate, lead diamyldithiocarbamate, zincdiamyldithiocarbamate, zinc dimethyldithiocarbamate, zincdiethyldithiocarbamate, zinc di-n-butyldithiocarbamate, zincpentamethylene dithiocarbamate, zinc ethylphenyldithiocarbamate,tellurium diethyldithiocarbamate, bismuth dimethyldithiocarbamate,selenium dimethyldithiocarbamate, selenium diethyldithiocarbamate,cadmium diethyldithiocarbamate, copper dimethyldithiocarbamate, irondimethyldithiocarbamate, diethylamine diethyldithiocarbamate,piperidinium pentamethylene dithiocarbamate and pipecolinepentamethylene dithiocarbamate; xanthogenic acid-type vulcanizationaccelerators such as sodium isopropylxanthogenate, zincisopropylxanthogenate and zinc butylxanthogenate; isophthalate-typevulcanization accelerators such as dimethylammonium hydrogenisophthalate; aldehyde amine-type vulcanization accelerators such asbutyraldehyde-amine condensation products andbutyraldehyde-monobutylamine condensation products; and mixturesthereof. The vulcanization accelerator can be present within a range offrom 0.1 to 15%, from 0.3 to 10%, or from 0.5 to 5%, by weight based onthe weight of the SBR polymer.

Antireversion agents can also be included in the vulcanization system toprevent reversion, i.e., an undesirable decrease in crosslink density.Suitable antireversion agents include zinc salts of aliphatic carboxylicacids, zinc salts of monocyclic aromatic acids, bismaleimides,biscitraconimides, bisitaconimides, aryl bis-citraconamic acids,bissuccinimides, and polymeric bissuccinimide polysulfides (e.g.,N,N′-xylenedicitraconamides). The antireversion agent can be present ina range of from 0 to 5%, from 0.1 to 3%, or from 0.1 to 2% by weightbased on the weight of the SBR polymer.

The above additives (antioxidants, antiozonants, prevulcanizationinhibitors, vulcanizing agents, vulcanization accelerators andantireversion agents) can be mixed with the SBR latex dispersion.Crosslinking agents can also be included in the vulcanization system insmall amounts to facilitate crosslinking of the SBR polymer chains andare typically organic peroxides. The SBR latex dispersion can bevulcanized at an elevated temperature and pressure and the vulcanizationprocess is well understood by those skilled in the art.

As noted above, the high temperature polymerized styrene-butadienecopolymer dispersions can be blended with low temperature polymerizedstyrene-butadiene copolymer dispersions produced at a temperature below40° C. (e.g., 5° C. to 25° C.). It is noted that the low temperaturepolymerized styrene-butadiene copolymer dispersions can be producedusing the method described above for the high temperature polymerizedstyrene-butadiene copolymer dispersions except at lower temperatures.

The high temperature styrene butadiene copolymers and dispersionsthereof can be used in various applications. For example, the hightemperature styrene butadiene copolymer can be used in vehicle tires,carpet backing, adhesives, foams, and paper coatings. In someembodiments, the high temperature styrene butadiene copolymers are usedin asphalt-based systems such as hot mix asphalt and asphalt emulsions.

In some embodiments, the high temperature styrene butadiene copolymercan be used in hot mix asphalt formulations. A polymer-modified hot mixasphalt can be prepared, for example, by blending asphalt and an aqueousdispersion of the high temperature polymerized styrene-butadienecopolymer at a blending temperature exceeding the boiling point ofwater. For example, the blending temperature can be 150° C. or greateror 160° C. or greater. The high temperature polymerizedstyrene-butadiene copolymer can be blended with a secondstyrene-butadiene copolymer as discussed herein. The polymer-modifiedhot mix asphalt composition is substantially free of water and can have,for example, a viscosity of 3000 cp or less, less than 2000 cp, or lessthan 1500 cp at 135° C. In some embodiments, the addition of the hightemperature styrene-butadiene copolymer, alone or in a blend, to the hotmix asphalt composition can result in an increase in viscosity of lessthan 125%, less than 100%, less than 75% or less than 50%. Thestyrene-butadiene copolymer can be present in an amount of from 0.5% to30% based on the total solids content of the styrene-butadiene copolymerand the asphalt. For example, the copolymer can be present in an amountof 1% or more, 1.5% or more, 2% or more, 2.5% or more, or 3% or more orcan be present in an amount of 25% or less, 20% or less, 15% or less,10% or less, 7.5% or less or 5% or less. In some embodiments, thepolymer-modified hot mix asphalt composition can have a viscosity ofless than 3000 cp at 135° C. when it includes 3% or more of thecopolymer (e.g. 3.5%, 4%, 4.5%, 5%, 5.5% or 6%). In addition, thecopolymers described herein have the potential to impart manageableviscosities to hot asphalt (e.g. at 135° C.) up to levels of 20 wt %latex polymer. As noted herein, the high temperature polymerizedstyrene-butadiene copolymer can be cured prior to being blended with theasphalt. In some embodiments, the high temperature polymerizedstyrene-butadiene copolymer can be blended with the asphalt and thencured. The polymer-modified hot mix asphalt formulations can be used forpaving to produce road surfaces or can be used in asphalt shingles.

In some embodiments, the high temperature styrene butadiene copolymercan be used in an asphalt emulsion. The polymer-modified asphaltemulsion includes the asphalt and the styrene-butadiene copolymerdispersed in the water with a surfactant. The polymer-modified asphaltemulsion can be produced by providing an aqueous asphalt emulsion andmixing the asphalt emulsion and an aqueous dispersion of the hightemperature styrene-butadiene copolymer. In some embodiments, theaqueous dispersion can further include a second styrene-butadienecopolymer as described herein. In some embodiments, the aqueousdispersion of the styrene-butadiene copolymer (optionally including thesecond styrene-butadiene copolymer) can be agglomerated to increase thesolids content. The styrene-butadiene copolymer can be present in anamount of from 0.5% to 30% based on the total solids content of thestyrene-butadiene copolymer and the asphalt. For example, the copolymercan be present in an amount of 1% or more, 1.5% or more, 2% or more, or2.5% or more or can be present in an amount of 25% or less, 20% or less,15% or less, 10% or less, 7.5% or less or 5% or less. The resultingasphalt emulsions can be used, for example, to maintain paved asphaltroad surfaces by employing different surface treatments including microsurfacing.

The following non-limiting examples are now provided. Except whereotherwise indicated, percentages are on a per weight basis and solutionsare aqueous solutions.

EXAMPLES Latex Preparation using Hot Polymerization

Styrene (50 parts by weight of the total monomers), tert-dodecylmercaptan (0.1 to 2.0 parts by weight of the total monomers), butadiene(50 parts by weight of the total monomers), and an aqueous solution ofsodium persulfate initiator (0.3 parts by weight of the total monomers),were added over 6 hours to a pre-heated reactor (70° C.) initiallycontaining water, sodium hydroxide (0.14 parts by weight of the totalmonomers), a polystyrene seed latex (1.66 parts by weight of the totalmonomers), and TRILON BX (0.03 parts by weight of the total monomers),an ethylenediaminetetraacetic acid commercially available from BASFCorporation (Florham Park, N.J.). The stabilization of the latexparticles during polymerization was accomplished by feeding an aqueoussolution of potassium oleate surfactant (3.6 parts by weight of thetotal monomers) over the course of the polymerization. The temperaturewas maintained at 70° C. throughout the polymerization reaction.Following the polymerization process, the latex dispersion was strippedof the residual monomers to provide an aqueous dispersion with residualstyrene levels of less than 400 ppm.

Latex Polymer-Modified Asphalt Sample Preparation

Asphalt cement was preheated to 160° C.+/−3° C. for at least two hoursand then 650 grams of the heated asphalt cement was poured into ametallic can. The asphalt-containing can was heated to 170° C.+/−3° C.using a heating mantle. A blade was inserted at an angle atapproximately 20° in the middle of the can to provide optimum mixing.The latex prepared according to the method described above was addedslowly to the hot asphalt with mixing at 300-325 rpm. Unless otherwisespecified, the amount of latex polymer solids added to the asphalt was 3wt % based on the total solids content of the latex polymer and asphalt.After each addition, time was allowed for most of the bubbling to ceaseand then the mixer speed was increased to approximately 400-700 rpm toblend the resulting mixture. After latex addition, the mixing wascontinued for two additional hours to achieve an equilibrated asphaltpolymer mixture. Samples of the polymer modified asphalts were taken forviscosity measurement or poured into molds for any desired testing.

SHRP Binder Testing of Latex Polymer-Modified Asphalt

The Strategic Highway Research Program (SHRP) evaluation of latexpolymer modified asphalts was carried out according to the ASTM D7175 orAASHTO T315 procedure on the original latex polymer modified asphalt, onthe latex polymer modified asphalt following Rolling Thin-Film Oven(RTFO) exposure, and also on the RTFO conditioned latex polymer modifiedasphalt that was conditioned in the Pressure Aging Vessel (PAV). TheDynamic Shear Rheometer (DSR) tests measure the dynamic shear modulusand stiffness of the latex polymer modified asphalt. In addition,Bending Beam Rheometer (BBR) testing was carried out according to ASTMD6678 or AASHTO T313 to measure the low temperature stiffnesscharacteristics of the latex polymer modified asphalt binders. Testingof the original (unaged or fresh) latex polymer modified asphalt and ofthe latex polymer modified asphalt after RTFO exposure provided the HighTemperature in the Performance Grade (PG) scale. Testing of the latexpolymer modified asphalt after RTFO and PAV exposure provided thestiffness at intermediate temperatures related to fatigue resistance andBBR testing after RTFO and PAV exposure provided the Low Temperature inthe PG scale.

Viscosity of Latex Polymer-Modified Asphalt

The viscosities of the latex polymer modified asphalts preparedaccording to the methods described above were measured according to ASTMD4402 or AASHTO T316 (American Association of State Highway andTransportation Officials).

Elastic Recovery of Latex Polymer-Modified Asphalt

The elastic recoveries of latex polymer modified asphalt bindersprepared according to the methods described above were measured using aductilometer according to a modified ASTM D6084 Procedure B testingprotocol.

Comparative Examples 1-2 and Examples 1-3

A styrene-butadiene copolymer, prepared by cold polymerizing (i.e., at atemperature of 25° C. or lower) styrene and butadiene, was provided asan aqueous dispersion (Polymer A). Polymer A has a number-averagemolecular weight (Mn) of 13,000 Daltons, a weight-average molecularweight of 507,000 Daltons, and a polydispersity of 39. Polymer B wasprepared by hot polymerizing 51% styrene and 49% butadiene at 70° C.Polymer C was prepared by combining 50 weight % of Polymer A with 50weight % of Polymer B, on a polymer solids basis, to form a resultingpolymer with a styrene-butadiene ratio of 36.6 to 63.4. Polymer C has anumber-average molecular weight (Mn) of 9,800 Daltons, a weight-averagemolecular weight of 373,000 Daltons, and a polydispersity of 38. PolymerA (3% by weight) was hot-mixed with Nustar 64-22, a commerciallyavailable asphalt from NuStar Asphalt Refining LLC (Savannah, Ga.)having a 64-22 performance grade, to provide Comparative Example 1.Polymer C (3% by weight) was hot-mixed with Nustar 64-22 asphalt toprovide Example 1. Comparative Example 2 was prepared by hot-mixingPolymer A (3% by weight) with Nustar 64-22 asphalt and 2.1 weight %(based on the total latex solids) active sulfur dispersion curing agentcontaining a vulcanization accelerator. Example 2 was prepared byhot-mixing Polymer C (3% by weight) with Nustar 64-22 asphalt and 2.1weight % (based on the total latex solids) active sulfur dispersioncuring agent containing a vulcanization accelerator. Example 3 wasprepared similarly to Example 2 except Polymer B was used in place ofPolymer C. NuStar 64-22 was provided as the control. The PG grades andviscosities for the asphalts were determined (Table 1).

TABLE 1 Comp. Comp. Control Ex. 1 Ex. 1 Ex. 2 Ex. 2 Ex. 3 PG Grades64-22 76-22 76-28 76-22 76-28 76-28 Passed SHRP Hi grade 64 76 76 76 7676 SHRP Lo grade −22 −22 −28 −22 −28 −28 Brookfield 654 2158 1409 23871466 1216 Viscosity (cps) Limiting High 69.5 80.7 77.1 79.6 77.6 76.2Temp (° C.) Limiting Low −26.4 −24 −28.1 −26.4 −28.6 −29.1 Temp (° C.)Temp Range 95.8 104.7 105.3 106.1 106.3 105.2 (° C.)

As shown in Table 1, the viscosities of the asphalt samples modifiedwith hot polymerized styrene-butadiene latexes (Examples 1, 2, and 3)decreased to an appropriate level as compared to the viscosities of theasphalt samples modified with the cold polymerized styrene-butadienelatexes (Comparative Examples 1 and 2). Also, the asphalts prepared withthe hot polymerized styrene-butadiene latexes (Examples 1, 2, and 3)displayed a higher performance grade than the asphalts prepared withcold polymerized latexes (Comparative Examples 1 and 2).

Comparative Example 3 and Example 4

Comparative Example 3 was prepared by hot-mixing Polymer A (3% byweight) with ERGON AC-20, an asphalt commercially available from Ergon,Inc. (Jackson, Miss.). Example 4 was prepared by hot-mixing Polymer C(3% by weight) with ERGON AC-20. The PG grades and viscosities for theasphalts were determined (Table 2).

TABLE 2 Comp. Ex. 3 Ex. 4 PG Grades Passed 64-22 64-22 SHRP Hi grade 6464 SHRP Lo grade −22 −22 Brookfield Viscosity (cps) 1446 963 LimitingHigh Temp (° C.) 69.7 67.9 Limiting Low Temp (° C.) −27.6 −26.7 TempRange (° C.) 97.4 94.6

As shown in Table 2, the viscosity of the asphalt sample modified with ahot polymerized styrene-butadiene latex (Example 4) decreased ascompared to the viscosity of the asphalt samples modified with the coldpolymerized styrene-butadiene latexes (Comparative Example 3). Theperformance grades of the asphalts were comparable.

Comparative Examples 1-2 and Examples 1-3 and 5

Comparative Examples 1-2 and Examples 1-3 were prepared as describedabove. Example 5 was prepared by hot-mixing Polymer B (3% by weight)with Nustar 64-22 asphalt. NuStar 64-22 was provided as the control. Theviscosities of the hot asphalt samples were determined (Table 3).

TABLE 3 Viscosity Identification Description (cp at 135° C.) ControlUnmodified asphalt sample 650 Comparative Polymer A (3 wt %) modifiedasphalt 2155 Example 1 sample Comparative Polymer A (3 wt %) modifiedasphalt 2387 Example 2 sample with curing agent (2.1 wt %) Example 1Polymer C (3 wt %) modified asphalt 1404 sample Example 2 Polymer C (3wt %) modified asphalt 1466 sample with curing agent (2.1 wt %) Example5 Polymer B (3 wt %) modified asphalt 1208 sample Example 3 Polymer B (3wt %) modified asphalt 1216 sample with curing agent (2.1 wt %)

As shown in Table 3, the viscosities of the asphalt samples modifiedwith hot polymerized styrene-butadiene latexes (Examples 1 and 5) werenot substantially different from the viscosities of the asphalt samplesmodified with hot polymerized styrene-butadiene latexes treated withcuring agent (Examples 2 and 3).

Examples 6-7

Example 6 was prepared by hot-mixing Ergon AC-20 asphalt with 3 wt % ofPolymer A, Polymer A with curing agent, and Polymer B. Example 7 wasprepared by hot-mixing NuStar 64-22 asphalt with 3 wt % of Polymer A,Polymer A with curing agent, and Polymer B. The viscosities of the hotasphalt samples were determined (Table 4).

TABLE 4 Asphalt Viscosity at 135° C. (cp) Polymer (3 wt %) in AsphaltExample 6 Example 7 Polymer A 1446 2155 Polymer A + curing agent (2.1%)1775 2387 Polymer B 733 1208

As shown in Table 4, the viscosities of the asphalt samples prepared byhot-mixing hot polymerized styrene-butadiene latexes (Polymer B)decreased as compared to those asphalt samples prepared by hot-mixingcold polymerized styrene-butadiene latexes with and without curing agent(Polymer A and Polymer A with curing agent). The asphalt samplecontaining Polymer B was 49% and 44% less viscous than the asphaltsample containing Polymer A for Ergon AC-20 and NuStar 64-22,respectively. Further, the asphalt sample containing Polymer B was 59%and 49% less viscous than the asphalt sample containing Polymer A and acuring agent for Ergon AC-20 and NuStar 64-22, respectively.

Comparative Example 4 and Examples 8-10

An asphalt emulsion comprising asphalt, water, one or more emulsifiersand Polymer A was prepared and 2.1 weight % curing agent, 4 parts of acationic surfactant and 2 parts of a non-ionic surfactant werepost-added to the emulsion to form Comparative Example 4. Example 8 wasprepared by mixing 80 parts of Polymer A with 20 parts of Polymer B,based on polymer solids, forming an asphalt emulsion comprising asphalt,water, one or more emulsifiers, Polymer A and Polymer B in theaforementioned ratio, and post-adding 2.1 weight % curing agent, 4 partsof a cationic surfactant and 2 parts of a non-ionic surfactant. Example9 was prepared by forming an asphalt emulsion comprising asphalt, water,one or more emulsifiers, Polymer C, and post-adding 2.1 weight % curingagent, 4 parts of cationic surfactant, and 2 parts of non-ionicsurfactant as in Example 8. Example 10 was prepared similarly to Example9 except Polymer B was used in place of Polymer C. The elastic recoveryand sweep performance for the asphalt emulsions were determined (Table5).

TABLE 5 Comp. Ex. 4 Ex. 8 Ex. 9 Ex. 10 Elastic Recovery (%) 57.5 60.058.3 53.3 Sweep Performance (%) 7.14 4.61 4.96 3.47

As shown in Table 5, the elastic recoveries of the asphalt emulsionscontaining hot polymerized styrene-butadiene latexes (Examples 8, 9, and10) were comparable to the asphalt emulsion containing a coldpolymerized styrene-butadiene latex (Comparative Example 4) and withinan acceptable range of greater than 50%. The sweep performances of theasphalt emulsions containing hot polymerized styrene-butadiene latexes(Examples 8, 9, and 10) were lower than the asphalt emulsion containinga cold polymerized styrene-butadiene latex (Comparative Example 4),demonstrating the hot polymerized styrene-butadiene containing emulsionspossess stronger binding properties.

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims and anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative composition materials and method stepsdisclosed herein are specifically described, other combinations of thecomposition materials and method steps also are intended to fall withinthe scope of the appended claims, even if not specifically recited.Thus, a combination of steps, elements, components, or constituents maybe explicitly mentioned herein; however, other combinations of steps,elements, components, and constituents are included, even though notexplicitly stated. The term “comprising” and variations thereof as usedherein is used synonymously with the term “including” and variationsthereof and are open, non-limiting terms. Although the terms“comprising” and “including” have been used herein to describe variousembodiments, the terms “consisting essentially of” and “consisting of”can be used in place of “comprising” and “including” to provide for morespecific embodiments and are also disclosed.

1. A method of making a styrene-butadiene copolymer dispersion,comprising: polymerizing styrene and butadiene in an aqueous medium at atemperature of 40° C. or greater to produce an uncured styrene-butadienecopolymer, wherein said polymerizing step occurs in the absence of acidmonomers and produces a non-carboxylated styrene-butadiene copolymer;and mixing a sulfur-based curing agent with the non-carboxylatedstyrene-butadiene copolymer, said curing agent allowing thenon-carboxylated styrene-butadiene copolymer to cure when exposed to anelevated temperature.
 2. The method of claim 1, further comprising thestep of curing the styrene-butadiene copolymer with the sulfur-basedcuring agent at an elevated temperature to produce a curednon-carboxylated styrene-butadiene copolymer.
 3. The method of claim 2,wherein said curing step comprises curing the styrene-butadienecopolymer with a sulfur-based curing agent and a vulcanizationaccelerator.
 4. The method of claim 1, wherein said polymerizing stepcomprises polymerizing styrene and butadiene in a weight ratio ofstyrene to butadiene of 20:80 to 80:20.
 5. The method of claim 1,wherein said polymerizing step comprises polymerizing styrene andbutadiene at a temperature of 50° C. or greater.
 6. The method of claim1, wherein said polymerizing step comprises polymerizing only styreneand butadiene monomers.
 7. The method of claim 1, wherein saidpolymerizing step comprises polymerizing styrene, butadiene, andacrylonitrile monomers.
 8. The method of claim 1, wherein saidpolymerizing step comprises polymerizing styrene and butadiene monomersin the presence of a molecular weight regulator.
 9. The method of claim1, wherein the resulting copolymer has a soluble portion that has aweight-average molecular weight as measured by Gel PermeationChromatography (GPC) of less than 400,000 g/mol.
 10. The method of claim1, wherein the resulting copolymer has a soluble portion that has aweight-average molecular weight as measured by Gel PermeationChromatography (GPC) of less than 200,000 g/mol.
 11. The method of claim1, wherein the resulting copolymer has a soluble portion that has anumber-average molecular weight as measured by Gel PermeationChromatography (GPC) of less than 20,000 g/mol.
 12. The method of claim1, wherein the resulting copolymer has a gel content of from 0% to 40%.13. The method of claim 1, wherein the resulting copolymer has a gelcontent of from 70% to 100%.
 14. The method of claim 1, furthercomprising modifying the copolymer dispersion to have an overallcationic charge by adding a cationic surfactant to the copolymerdispersion.
 15. The method of claim 1, wherein the polymerization occursin a single stage process.
 16. A styrene-butadiene copolymer, comprisingstyrene and butadiene monomer units, wherein said copolymer is curedwith a sulfur-based curing agent, is non-carboxylated, and ispolymerized at a temperature of 40° C. or greater.
 17. The copolymer ofclaim 16, wherein the cis-1,4 butadiene units are greater than 20% andthe trans-1,4 butadiene units are less than 60% of the total number ofbutadiene units in the copolymer.
 18. The copolymer of claim 16, whereinthe weight ratio of styrene to butadiene monomer units is 20:80 to80:20.
 19. The copolymer of claim 16, wherein said copolymer is derivedfrom only styrene and butadiene monomers.
 20. The copolymer of claim 16,wherein said copolymer is derived from styrene, butadiene andacrylonitrile monomers.
 21. The copolymer of claim 16, wherein saidcopolymer is derived from styrene and butadiene monomers and a molecularweight regulator.
 22. The copolymer of claim 16, having a solubleportion that has a weight-average molecular weight as measured by GelPermeation Chromatography (GPC) of less than 400,000 g/mol.
 23. Thecopolymer of claim 16, having a soluble portion that has aweight-average molecular weight as measured by Gel PermeationChromatography (GPC) of less than 200,000 g/mol.
 24. The copolymer ofclaim 16, having a soluble portion that has a number-average molecularweight as measured by Gel Permeation Chromatography (GPC) of less than20,000 g/mol.
 25. The copolymer of claim 16, having a gel content offrom 0% to 40%.
 26. The copolymer of claim 16, having a gel content offrom 70% to 100%. 27-28. (canceled)
 29. An aqueous dispersion comprisingwater and the copolymer of claim
 16. 30. The aqueous dispersion of claim29, further comprising a cationic surfactant to produce a dispersionhaving an overall cationic charge.
 31. A method, comprising mixing anaqueous dispersion comprising a copolymer of claim 16 having at leastone first surfactant and an aqueous dispersion of a secondstyrene-butadiene copolymer polymerized at a temperature of less than40° C. and having at least one second surfactant, wherein the at leastone first surfactant and the at least one second surfactant include atleast one common surfactant.
 32. The method of claim 31, furthercomprising the step of curing the mixture of said mixing step. 33-46.(canceled)